1. Field of the Invention
The present invention relates to a pneumatic device, in particular to a telescopic pneumatic device.
2. Description of the Related Art
Shown in FIG. 1 is a generally known telescopic pneumatic device. Such pneumatic device comprises a vertical tubular outer cylinder 21 and an annular lower end cap 22, a leak-preventing washer 23 and a sleeve 24 sequentially disposed in that order of arrangement from the bottom end of the outer cylinder 21, a tubular inner cylinder 25 coaxially disposed in the outer cylinder 21 and abutting the top end of the sleeve 24, a vertically movable piston 26 mounted in the inner cylinder 25, a piston rod 27 connected to the piston 26 and extending downwardly out of the outer cylinder 21, an upper end cap 28 provided at the top end of the inner cylinder 25, and control means 29 mounted in the upper end cap 28.
The inner and outer air chambers 20,10 defined by the inner and outer cylinders 25, 21, respectively, are filled with compressed gas, and the control means 29 controls the flow of the compressed gas in the inner and outer air chambers 20,10 and, in turn, controls the length of the piston rod 27 that protrudes out of the outer cylinder 21.
However, during assembly and machining of the above-described pneumatic device, the steps involved in the assembly of the control means 29 and the upper end cap 28 are too many and complex, and the machining cost of the upper end cap 28 is high. In addition, since most inner cylinders are generally made of steel material, in order to enable the piston 26 which is mounted in the inner cylinder 25 to slide smoothly in movement and to avoid occurrence, during use, of even greater wearing of the sealing gasket which is disposed around the piston 26, which is caused by too much frictional force subjected to the internal wall of the inner cylinder 25, the requirement for smoothness and fineness of the internal wall of the steel inner cylinder 25 is usually higher. In view of this, the cost of the machining process for the steel inner cylinder 25 is high. Compounded with the increasing prices of steel with the passing of time, the overall manufacturing costs for the telescopic pneumatic device is extensively increased.